1. Field of the Invention
The present invention relates to a process for producing a recording head and to a head obtained by said process. It is used in magnetic recording on supports having a very limited width of approximately 1 micron or less.
2. Background Discussion
The magnetic head according to the invention is of the horizontal, thin film type, such as is e.g. described in EP-A-0 152 326. More particularly, the invention improves a process for the production of such heads known from FR-A-2 604 028 (or its corresponding EP-O 262 028 and U.S. Pat. No. 4,837,924.)
FIG. 1 shows the structure obtained by this process. It is possible to see a generally silicon substrate 10, in which is embedded a lower pole piece 16 formed by electrolytic deposition on an electrode 14, a double conducting coil 20, two magnetic pillars 23,24, each surrounded by a part of the coil, an upper pole piece formed by two flux separators 30,31 separated by a central, amagnetic island 32 and finally two pole pieces 46,48 separated by an amagnetic spacer 42 defining a gap.
The gap width is approximately 20 microns and the thickness of the pole pieces 46,48 is a few microns (FIG. 1 being substantially to scale with respect to the upper part).
Although satisfactory in certain respects, such a magnetic head has certain disadvantages. Firstly, when the width of the track to be read decreases and reaches values equal to or below 1 micron, the magnetization of the magnetic layer in the inoperative state under the effect of the very marked shape anisotropy of the upper pole piece, tends to be oriented parallel to the large dimensions of the pole piece. Therefore the permeability of the pole piece decreases. In addition, the magnetic layer can break up into portions, so that on reading, there is a significant wall noise.
The first of these effects leads to a reduction in the amplitude of the signal and the second to a reduction in the signal-to-noise ratio and are highly prejudicial for the limited track widths, where the reading signal is already intrinsically small.
Another noise increase comes that part of the coil projecting to either side of the upper pole pieces. Although further from the track than the upper piece and only offering a lower resolution than that of the air gap, the lateral portions of the coil still trap a parasitic flux from the tracks adjacent to the track read. This leads to a not completely negligible noise level in view of the small track widths.